In an image sensor according to the related art, color filters are generally formed in a Bayer array.
However, in the Bayer array, because light absorbed by each color filter cannot be used for photoelectric conversion, use efficiency of the light may be degraded by an amount corresponding to the color filters.
Therefore, for the purpose of raising use efficiency of light more than the color filters of the Bayer array to achieve high sensitivity or high resolution, a longitudinal spectroscopic image sensor in which a plurality of photodiodes are stacked in the same pixel has been suggested (for example, refer to Patent Documents 1 to 3).
In the longitudinal spectroscopic image sensor using a silicon substrate, the photodiodes are stacked at different depths in silicon to perform a color separation using that an absorption wavelength of light is different depending on a depth of the silicon substrate.
In addition, the charge is transferred to a surface of the silicon substrate through a charge transfer path (hereinafter, referred to as an “implantation plug”) formed by impurity implantation and having a charge gradient to read the charge from the photodiode formed in a deep portion of the silicon substrate.
Meanwhile, the charge that is accumulated in the photodiode near the surface of the silicon substrate is read to a floating diffusion using a transfer gate.
In the longitudinal spectroscopic image sensor having the above-described structure, when light leaks into the implantation plug or a field accumulation region near the surface, photoelectric conversion is generated by the leaked light.
However, because a wavelength component of the leaked light is different from a wavelength component of light on which photoelectric conversion is executed by a photodiode connected to the implantation plug, the charge by the light of the different wavelength components is mixed and color mixture is generated.
Therefore, a light shielding film needs to be formed on the implantation plug to perform superior color separation by preventing the color mixture from being generated.
Meanwhile, if the light shielding film is formed on the implantation plug, an aperture ratio on the photodiode decreases by an amount corresponding to the implantation plug and sensitivity decreases, as compared with a configuration of a photodiode of a single layer in which the implantation plug is not formed.
That is, in the structure of the longitudinal spectroscopic image sensor according to the related art, the merit of the superior use efficiency of the light cannot be utilized. In addition, because the aperture ratio decreases and the sensitivity decrease, the merit of the longitudinal spectrum cannot be utilized.